a. Field of the Invention
The present invention relates to novel biocompatible polysaccharide gel compositions, methods of their manufacture and use, and the novel crosslinkers used to make them. More specifically, the present invention relates to novel compositions of hyaluronic acid gels that are crosslinked with a novel multifunctional crosslinker, and to methods of making such crosslinked hyaluronic acid gels.
b. Background Art
Hyaluronic acid is a non-sulfated glycosaminoglycan that is distributed widely throughout the human body in connective, epithelial, and neural tissues. Hyaluronic acid is also a major component of skin, where it is involved in tissue repair. As skin ages and is repeatedly exposed to the sun's ultra violet rays, dermal cells decrease their production of hyaluronic acid and increase the rate of its degradation. Likewise, aging skin loses collagen, another natural substance necessary to keep skin youthful and resilient. Over time, the loss of hyaluronic acid and collagen causes aging skin to develop lines, wrinkles, and folds.
In the past several years, compositions of hyaluronic acid have been used in cosmetic applications to fill wrinkles, lines, folds, scars, and to enhance dermal tissue, for example, to plump lips. Because hyaluronic acid is natural to the human body, it is a generally well tolerated and fairly low risk skin augmentation product.
Originally, hyaluronic acid compositions contained particles, or microspheres, of hyaluronic acid suspended in a gel. These compositions, which are still in commercial use, tend to degrade within a few months after injection and thus require fairly frequent reinjection to maintain their skin augmenting effect. Specifically, hyaluronic acid is highly soluble in its natural state and has a rapid turnover through enzymatic and free radical metabolization.
More recently, compositions of cross-linked hyaluronic acid have been used for dermal augmentation. These hyaluronic acid compositions are typically crosslinked with a bifunctional crosslinking agent, such as butanediol diglycidyl ether (BDDE), typically with a double ether bond connecting the HA molecules to form a less water soluble polymer hydrogel network that is more resistant to degradation, and thus requires less frequent reinjection, than the non-crosslinked hyaluronic acid compositions. Some such cross-linked compositions contain fairly large particles, around approximately 50-1000 μm each, of hyaluronic acid suspended in a gel. Others are a fairly uniform consistency gel matrix of hyaluronic acid.
While these known crosslinked hyaluronic acid compositions last longer than their noncrosslinked counterparts, their duration is typically twelve months or less, thus still requiring fairly frequent reinjection. It is thus desirable to develop a hyaluronic acid composition that is biocompatible and useful as a dermal filler, but has a longer useful lifetime upon injection. Specifically, it is desirable to develop a hyaluronic acid composition that is biocompatible and injectable, but that has a higher mechanical strength, a greater resistance to enzymatic degradation, and a higher water retention than currently available compositions.